Consider null an error value during mysql verification

Related: PROD-27845 (PROD:27845)

Change-Id: Ie33725c40c337fe0ffa47c4d7f2aa5cadb907b6d
(cherry picked from commit 79810268d12bbaa6ac93dbdaa901d09dacf50349)
diff --git a/src/com/mirantis/mk/Galera.groovy b/src/com/mirantis/mk/Galera.groovy
index 7627077..5793632 100644
--- a/src/com/mirantis/mk/Galera.groovy
+++ b/src/com/mirantis/mk/Galera.groovy
@@ -170,7 +170,7 @@
     for (key in parameters.keySet()) {
         param = parameters.get(key)
         if (key == 'wsrep_local_recv_queue_avg' || key == 'wsrep_local_send_queue_avg') {
-            if (param.get('actualValue') > param.get('expectedThreshold').get('error')) {
+            if (param.get('actualValue') == null || (param.get('actualValue') > param.get('expectedThreshold').get('error'))) {
                 param << [match: 'error']
             } else if (param.get('actualValue') > param.get('expectedThreshold').get('warn')) {
                 param << [match: 'warn']